Metal oxyanion coated substrates

ABSTRACT

Layered metal oxyanion coated substrates are disclosed comprising a three dimensional inorganic substrate having a coating of metal oxyanion derived from a pre-associated coating on at least a portion of all three dimensions thereof, produced by a unique process having particular applicability to the manufacture of metal oxysulfide, oxycarbide and oxynitride coated three dimensional substrates. Certain novel coated substrates, such as flakes, spheres and porous substrate are disclosed. The coated substrates are useful in polymer catalysis, heat dissipation and shielding applications.

BACKGROUND OF THE INVENTION

The present invention relates to a process for coating powder particlesubstrates, the coated powder particle substrates and to applicationsand uses thereof. More particularly, the invention relates to coatingpowder particle substrates with a metal oxyanion containing material,such material preferably being an electrically and/or thermallyconductive oxyanion containing material and such coated powdersubstrates.

In many applications using powder it would be advantageous to have anelectrically and/or thermally conductive; radiation absorbing and/orimproved mechanical oxyanion coatings which are substantially uniform,have high and/or designed conductivity and/or radiation absorbingproperties and/or improved mechanical properties and have good chemicalproperties, e.g., morphology, stability, corrosion resistance, etc.

A number of techniques have been employed to provide certain metaloxyanion coatings on fixed generally larger size substrates. Forexample, the CVD processes are well known in the art for coating asingle flat surface, which is maintained in a fixed position during thecontacting step. The conventional CVD process is an example of a“line-of-sight” process or a “two dimensional” process in which themetal oxyanion is formed only on that portion of the substrate directlyin the path of the metal source as metal oxyanion is formed on thesubstrate. Portions of the substrate, particularly internal and externalsurfaces, which are shielded from the metal oxyanion being formed, e.g.,such as the opposite side and edges of the substrate which extendinwardly from the external surface and substrate layers which areinternal or at least partially shielded from the depositing metaloxyanion source by one or more other layers or surfaces closer to theexternal substrate surface being coated, do not get uniformly coated, ifat all, in a “line-of-sight” process. Such shielded substrate portionseither are not being contacted by the metal source during line-of-sightprocessing or are being contacted, if at all, not uniformly by the metalsource during line-of-sight processing. A particular problem with“line-of-sight” processes is the need to maintain a fixed distancebetween the source and the substrate. Otherwise, metal oxyanion can bedeposited or formed off the substrate and lost, with a correspondingloss in process and reagent efficiency.

There has been a need to develop processes for producing metal oxyanioncoated powder substrate particles and processes, particularly under fastreaction processing conditions, which provide short processing timesrequired for producing high quantities of metal oxyanion coated powderparticle substrates and to produce unique metal oxyanion coated powdersubstrates having improved properties

BRIEF SUMMARY OF THE INVENTION

A new process, e.g., a “non-line-of-sight” or “three dimensional”process, useful for coating of three dimensional powder particlesubstrates has been discovered. As used herein, a “non-line-of-sight” or“three dimensional” process is a process which coats surfaces of apowder substrate with a metal oxyanion coating which surfaces would notbe directly exposed to metal oxyanion forming compounds being depositedon the external surface of the substrate during the first line-of-sightcontacting step. In other words, a “three dimensional” process coatscoatable powder substrate surfaces which are at least partially shieldedby other portions of the powder substrate which are closer to theexternal surface of the powder substrate and/or which are further fromthe metal oxyanion forming source during processing, e.g., the internaland/or opposite side surfaces of for example glass, ceramic or mineralpowder particle substrates such as fibers, spheres, flakes or othershapes or surfaces including porous shapes.

A new fast reaction, elevated temperature process for coating a threedimensional powder substrate having shielded surfaces with a metaloxyanion, preferably a conductive or radiation absorbing or mechanicallyimproved metal oxyanion coating on at least a part of all threedimensions thereof and on at least a part of said shielded surfacesthereof has been discovered. In brief, the process comprises forming areaction mixture comprising powder substrate particles, a metal oxyanionprecursor, for example, silicon, aluminum, boron, zirconium, lanthanumand titanium precursors, such as oxide, partial oxide and chloridecontaining precursors, an anion forming precursor said metal and theanion of said precursors being chemically different and an oxy precursorchemically the same or different than one or both of said metal oxyanionand anion forming precursor and reacting the reactant mixture under fastreaction short residence time, high temperature conditions in a reactionzone to form a metal oxyanion coated substrate and recovering suchcoated substrate, preferably a conductive or radiation absorbing ormechanically improved oxyanion containing coated substrate.

The anion forming precursor is typically a precursor agent that providesthe anion portion of the metal such as boron, nitrogen, silicon, carbonand sulfur. The anion forming precursors can be in the form of a gas,liquid or solid for example methane and carbon powder as a source forcarbon, nitrogen and ammonia as a source for nitrogen, boron halidessuch as boron trichloride as a source for boron, sulfur halides andhydrogen sulfide as a source for sulfur and various silicon halides andhydrosilicides as a source for silica.

The forming of the metal oxyanion precursor/substrate, the oxy precursorand anion forming precursor reactant mixture preferably takes placeclosely in time to reacting in the reaction zone. In a particularlypreferred embodiment, the reaction mixture after formation is introduceddirectly into the high temperature reaction zone under fast reactionprocessing reducing conditions. The coated powder substrate is thenrecovered by conventional means.

The process can provide unique coated substrates including single andmixed oxyanions which have application designed conductivity and/orabsorbing properties and/or improved mechanical properties so as to besuitable for use as components such as additives in a wide variety ofapplications. Substantial coating uniformity, e.g., in the thickness ofthe metal oxyanion coating is obtained. Further, the present metaloxyanion coated substrates in general have outstanding stability, e.g.,in terms of electrical, thermal and mechanical properties and morphologyand are thus useful in various applications.

DETAILED DESCRIPTION OF THE INVENTION

The present coating process comprises forming a reactant mixture of apowder substrate, a metal oxyanion precursor, such as metal partialoxide and/or chloride forming components, metal complexes and mixturesthereof, an anion forming precursor and an oxy precursor and reactingthe reactant mixture, at fast reaction, elevated temperature processconditions, preferably reducing conditions, effective to form a metaloxyanion coating on the powder substrate. The components of the reactantmixture are reacted at conditions effective to convert the metaloxyanion precursor to metal oxyanion and form a metal oxyanioncontaining coating, preferably a conductive, or radiation absorbingmetal oxyanion containing coating, on at least a portion of the threedimensions of the substrate. The process as set forth below will bedescribed in many instances with reference to various compounds ofsilica, titanium, aluminum, zircomium and boron which have been found toprovide particularly outstanding process and product properties.However, it is to be understood that other suitable metal oxyanionprecursors are included within the scope of the present invention.

As set forth above the reactant mixture is subjected to fast reactionprocessing conditions at elevated temperatures in order to form a metaloxyanion coating on the substrate. The reactant mixture preferablyshould be formed prior to high temperature fast reaction processingconditions. This reduces metal oxyanion precursor forming off of thesubstrate which decreases the yield of metal oxyanion coated substrate.By “forming” is meant that the metal oxyanion precursor is preferablyassociated with the powder substrate before deleterious reaction of themetal oxyanion precursor with the oxy precursor and/or anion formingprecursor can take place off the substrate, such as not to be associatedwith the substrate as a coating. It has been found that the preferredreactant mixtures are those that are formed proximate in time to theintroduction of the reactant mixture into the high temperature fastreaction zone. Thus for example, the reactant mixture can be a liquidslurry wherein the metal oxyanion precursor is soluble in the liquidand/or an insoluble solid in the liquid slurry. Further, the liquidslurry can be a suspension of the metal oxyanion precursor. The metaloxyanion precursor preferably is a precipitate on the substrate in theliquid solid slurry. Further the reactant mixture can be a solid orflowable powder form such as a precursor powder and/or precipitateand/or liquid film coating of metal oxyanion precursor. Each of theabove reactant mixtures can offer unique and distinct processing productadvantages in the process of this invention. The liquid slurry reactantmixtures are preferably atomized, such as gas atomized, uponintroduction with the substrate into the reaction zone for conversion tothe metal oxyanion coated substrates. Further, the flowable powderreactant mixtures such as metal oxyanion precursor powder, precipitateand/or liquid film reactant mixtures, can be air fluidized into thereaction zone or gravity or mechanically fed into the reaction zone. Forliquid reactant mixtures, it is preferred to maximize the concentrationof the substrate in the liquid slurries on a wt % basis so as tomaximize the association of the metal oxyanion precursor with thesubstrate. It is preferred that the concentration of substrate in liquidslurries be from about 10 to 65 wt % more preferably from about 30 to 60wt % or higher. As is recognized by those of skill in the art, theviscosity of the slurries will vary as a function of the particle size,its geometry and density. Viscosities are used which allow for overalloptimum process efficiencies on a product quality and throughput basis.

The anion forming precursor can be a gas, liquid or a solid. As setforth above the anion forming precursor can be a gas such as methane,chloro methanes and ethanes, nitrogen, ammonia, boron trichloride,hydrogen sulfide and the like. The anion forming precursor associateswith the metal oxyanion precursor/substrate and oxy precursor at andduring the reactions in the reaction zone. For example the anion formingprecursor in the form of a gas can be at least a part of the carrier gasused to atomize and/or fluidized the substrate metal oxyanion precursor.Further, the anion precursor gas can be introduced into the reactionzone with the metal oxyanion precursor substrate such that reactiontakes place for the conversion to metal oxyanion coating on thesubstrate. In addition the anion forming precursor can be in the form ofa solid such as a powder which is also associated with the substratesimilar to or the same as the metal oxyanion precursor. As set forthabove, there is an intimate association of the metal oxyanion, oxyprecursor and anion forming precursors in order for fast reactionconversion to the metal oxyanion coating on the substrate to occur atthe short residence time, high temperature conditions in the reactionzone.

The fast reaction processing conditions as set forth above include avery short reaction residence time for the powder particles in theelevated temperature reaction zone. “Reaction zone” is defined as thatzone at elevated temperature wherein fast reaction of the metal oxyanionprecursor with the oxy precursor and anion forming precursor takes placeon the substrate such that the metal oxyanion precursor is notsubstantially lost as separate metal oxyanion particles not associatedwith the substrate. Thus the reaction zone allows for association of themetal oxyanion precursor on the substrate wherein subsequent processingwill not substantially adversely affect the overall metal oxyanioncoating on the substrate. It is important that the residence time in theelevated temperature reaction zone associate the metal oxyanionprecursor with the substrate. It is contemplated within the scope ofthis invention that further processing such as conditions to promotefurther reduction, uniform crystallinity and/or coating densificationcan be carried out according to the process of this invention.

The fast reaction processing conditions in the reaction zone can vary asto temperature and residence time according to the physical and chemicalproperties of the metal oxyanion precursor and substrate. The averageparticle residence time in the reaction zone is less than about onesecond preferably from about 0.5 milliseconds to about 1 second, morepreferably from about 1 millisecond to about 500 milliseconds and stillmore preferably from about 5 milliseconds to about 250 milliseconds.Further, the residence time can be defined by the particle velocity inthe reaction zone. Preferably the average particle velocity in thereaction zone is from about three to about 30 meters/second, morepreferably from about three to about 10 meters/second.

The elevated temperature in the reaction zone is maintained by a thermalsource that rapidly transfers thermal energy to the reactant mixture.The unique combination of reactant mixture, short residence time and athermal source for rapid thermal transfer provides for rapid associationof the metal oxyanion precursor with the substrate on both external andshielded surfaces without substantially adversely effecting the solidintegrity of the substrate. By the term solid integrity is meant thatthe substrate retains at least a part preferably a majority an even morepreferably a substantial majority of the substrate as a solid under thetemperature conditions in the reaction zone. Depending on the physicaland chemical properties of the substrate the surface and near surface ofthe substrate can become reactive and/or melt under the thermalconditions in the reaction zones. The highly reactive surface and/orrapid melting and solidification for certain substrates can provideenhanced properties associated with the metal oxyanion coating such asbarrier properties, binding properties and preferential crystallinesurface formation by the substrate. The short residence times in thereaction zones allow for rapid chemical reactions and rapid quench whenthe substrate particles leave the reaction zone.

One of the unique advances of the process of this invention is theformation of very thin metal oxyanion coatings on powder substrateswithout substantially adversely affecting the solid integrity of thesubstrate, i.e. the inner core of the substrate is essentiallychemically unaltered. Thus, the metal oxyanion precursor associated withor formed from the substrate as a thin film and/or the outer surface ofthe substrate has a reactive surface which exhibits high reactivity as aprecursor and provides for the formation of the metal oxyanion coatingunder fast reaction processing conditions. Thus, only the thin filmmetal oxyanion precursor and/or reactive surface on the substrate haveto be converted via reaction with the oxy precursor and anion formingprecursor. As set forth above, the substrate retains an inner core ofessentially the same chemical composition as the original startingsubstrate. Thus, in the preferred embodiment of this invention, themetal oxyanion precursor can be for example a preassociated flowablepowder, i.e. a precoat of a powder, precipitate or film forming liquidor the surface itself of the substrate where thin film reaction with theoxy precursor and anion forming precursor takes place in the reactionzone. Typical examples of substrate coating surface reaction on at leasta part of all three dimensions thereof are oxycarbonation andoxynitridation of aluminum, boron and titanium oxides or partial oxides.

The thermal source produces elevated temperatures that allow for thereactant mixture to rapidly produce metal oxyanion coated substrates andallows residence times that provide for the association of the metaloxyanion precursor with the substrate and reaction with the oxyprecursor and anion forming precursor. Thus the thermal source mustallow for control of the elevated temperature to produce metal oxyanioncoated substrates and a residence time which allows the chemicalreactions and/or association of the metal oxyanion precursor with thesubstrate to take place on the substrate. The preferred thermal sourceswhich allow for control of elevated temperatures and the residence timesnecessary for chemical reaction and/or association of the metal oxyanionprecursor with the substrate are induction plasma sources preferably RFinduction plasma sources and flame combustion sources.

As set forth above, the thermal source provides an elevated temperaturethat primarily acts on the metal oxyanion precursors, oxy precursor andanion forming precursor such that the powder substrate, primarily theinternal portions of the substrate are at a lower temperature than theexternal temperature in the reaction zone. As will be more fullydescribed below, the typical substrate can have a relatively low heattransfer coefficient which when combined with the short residence timesin the reaction zone allows for such differential between the externaltemperature and the internal temperature of the substrate. Further theprocessing conditions can be adjusted to take advantage of this thermalgradient particularly as to selective reaction of the anion formingprecursor on the surface, melting and resolidification andcrystallization on the surface and near surface of the substrate.Further, the temperature within the reaction zone is controlled to allowrapid reaction of the metal oxyanion precursors, oxy precursor and anionforming precursor which reactions can increase substantially theassociation of the coating with the substrate and yields, i.e. reducedtendency towards volatilization and further the completion of theoverall reaction to metal oxyanion coating. As set forth above, one ofthe major advances is the association of the metal oxyanion precursorcoating through the reaction zone into the quench stage. The recoveredmetal oxyanion coated substrates can be further annealed for furtherdensification, crystallization and minimizing the presence ofdeleterious amounts of contaminants such as oxygen.

RF inductively coupled plasma systems are well known to those ofordinary skill in the art and typically consist of an RF power generatorsupplying a RF current to an induction coil wound around a plasmaconfinement tube. The tube confines the plasma discharge. Power levelsfor plasma systems can vary from about 10 kW up to about 500 kW. Typicalfrequencies vary from about 0.3 MHz to even as high as 14 MHz. Typicalranges are in the 0.3 to 5 range.

The plasma system typically uses three different gases including acentral gas sometimes referred to as a central swirl gas used primarilyfor formation of the plasma, a sheath gas used primarily to stabilizeand center the plasma and a third carrier gas which typically is used totransport a powder feed and/or atomize a liquid slurry feed. As isrecognized by those of ordinary skill in the art, the composition of allthree gases can vary and can include gases such as argon, nitrogen,hydrogen and oxygen as well as other gases such as anion formingprecursor gases. In addition mixtures of varying gases can be useddepending on the characteristics of the plasma that is required for theprocess. As set forth above, a component of the plasma gases can serveas an anion forming precursor, the oxy precursor and a reducing agent.In other cases, a secondary gas can be injected into the plasma orsheath surrounding the plasma to provide the anion forming precursorand/or oxy precursor. The gases used as sheath, central and carriergases can be different or the same and mixtures of different gases canbe used. For example, a reducing gas can be used for the sheath, centraland carrier gas or various other gases, such as argon, can be combinedwith the sheath or central gas.

As set forth above the oxy precursor can be chemically the same ordifferent than one or both of said metal oxyanion and anion formingprecursors. Thus for example, the oxy precursor can be derived from themetal oxyanion precursor when for example the metal oxyanion precursorcontains oxygen such as a metal oxide or metal partial oxide. Further,the oxy precursor can be chemically the same as the anion formingprecursor when for example the anion forming precursor also contains theoxy precursor such as nitrogen oxides that can decompose into a nitrogenoxide and oxygen, such as the decomposition of nitrous oxide to oxygenand nitric oxide. Further the oxy precursor can be oxygen such as oxygencontained in air. For example metal chlorides as set forth above can beformed into a reaction mixture with ammonia and oxygen to form anoxynitride. Further metal oxides can be combined with, for example,ammonia, and/or ammonia and hydrogen and/or hydrogen and nitrogen toform a metal oxynitride. As set forth above a reducing atmosphere can beused to facilitate the formation of the metal oxyanion products. Forexample metal oxides can be combined with a carbon source such as a lowmolecular weight gas such as methane or ethane and hydrogen to form ametal oxycarbide. Still further examples are mixed metal oxyanions thatcan be formed from mixtures of metal oxyanion precursors. For examplealuminum trichloride and silica tetrachloride can be combined withammonia and oxygen to form a silica aluminum oxynitride.

The gas flow rates for the central, sheath and carrier gases can varyover a wide range with such ranges being adjusted to within theresidence time and particle velocities required for the conversion ofthe metal oxyanion precursor to coated metal oxyanion substrate. Ingeneral the rate of introduction of the sheath, central and carriergases will vary with typically the sheath gas being introduced at a rateof from about three to about five times that of the central swirl gas.In addition, the central swirl gas rate will generally be higher thanthe carrier gas since the carrier gas is used to control the rate atwhich the reactant mixture is introduced into the reaction zone. The gascompositions and flow rates can be optimized to provide desired processconditions. For example, nitrogen can be introduced into the central gasin order to lower the overall temperature profile within the reactionzone. Typically the other gas rates and/or partial pressure within thegiven gas composition are lowered in order to control the particleresidence time and particle velocities within the reaction zone.Further, the anion forming precursor and oxy precursor content in thevarious gases within the reaction zone can be adjusted to provide nearstochiometric quantities or slight excess in order to limit the amountpresent in the later portion and tail of the reaction zone. In addition,anion forming and oxy precursor enrichment can take place such as theintroduction of anion forming precursor at the tail of the reaction zoneto provide enhanced overall reaction conditions prior to quench.Typically, the enthalpy of the gas composition is controlled so as tomaintain the elevated temperature that promotes rapid reaction of themetal oxyanion precursors with the oxy precursor and anion formingprecursor on the substrate. Thus the enthalpy of components such ashydrogen and organic components added as part of the liquid slurry andpowder reaction mixtures are taken into consideration for defining thetemperature required in the reaction zone. Further, the gas rates(volume of gas per unit time) will vary depending on the size and designof the process equipment. As set forth above, the residence times arelong and the particle velocities slow when compared to typical sonic andsupersonic plasma type systems. As is set forth above, the oxy precursorand anion forming precursor under thermal process conditions allow forthe reaction of metal oxyanion precursor to metal oxyanion coating onthe substrate to take place within the reaction zone. It has been foundthat the residence times and/or particle velocities as set forth abovetogether with the control of gas composition and temperature conditionsallow for the reactions to take place on the substrate to produce themetal oxyanion coated substrates. The control by the thermal source ofthe temperature in the plasma or adjacent to the plasma, i.e. reactionzone, allows for the reactions to take place while not substantiallyadversely effecting the solid integrity of the substrate. Further, thetemperature and the dimension of the plasma can be adjusted so as toprovide selective reaction with the oxy precursor and anion formingprecursor and/or melting on the surface or near surface of the substrateto enhance overall reaction, bonding and uniformity of the metaloxyanion coating on the substrate. As set forth above, the temperature,particle residence time and oxy precursor and anion forming precursorconcentration allow for the conversion of the metal oxyanion precursorto metal oxyanion coating while not adversely effecting the solidintegrity of the substrate. Thus, the temperature within the reactionzone can vary according to the above process conditions and typicallyare in the range of from about 1000° K to about 4500° K, more preferablyfrom about 1500° K to about 3500° K. As set forth above, the temperaturecan be moderated by auxiliary gases including inert gases.

The reactant mixture can be introduced into the plasma at varyinglocations within the plasma including the tail, i.e. terminal, portionof the plasma flame. The reactant mixture in addition can be introducedlaterally into or adjacent to the plasma flame and/or the tail of theplasma flame or at varying angles to the plasma including perpendicularto the plasma or the plasma tail. In a typical system configuration aprobe of appropriate metallurgy such as inconel, is centrally mounted inthe plasma confinement tube. Typically a quartz tube is interposedbetween the probe and the confinement tube. The central gas in injectedinto the quartz tube and the sheath gas is injected in the annularpassage defined between the quartz tube and the plasma confinement tube.Conventional cooling of the system is used. The reactant mixture feedprobe can be used to gas atomize the liquid slurry reaction mixtures ofthis invention and/or gas atomize, such as with an inert and/or anionforming precursor gas and mixtures thereof, the powder feeds of thisinvention. For example, in the liquid slurries, fine droplets of theliquid slurries can be injected typically into the central portion of oradjacent to the plasma discharge. Further, the position of the injectionprobe within or adjacent to the plasma for powder or liquid slurries canbe varied such as to optimize the performance and overall yields ofmetal oxyanion coated substrates. As is set forth above, the reactionmixture can be introduced into the tail of the plasma discharge such aslaterally or at an angle into the plasma tail. It is preferred that thereactant mixtures from liquid slurries to powders be introduced into thereaction zone with a carrier gas, particularly an inert and/or reducingand/or oxy precursor and/or anion forming precursor containing carriergas and mixtures thereof which enhances the rate of reaction of themetal oxyanion precursor to metal oxyanion coating on the substrate. Thepowders can be gravity fed and/or continuously fed such as by screwfeeders into the plasma. In a preferred embodiment of this invention,the concentration of the substrate in the liquid slurries can bemaintained at a relatively high concentration such as from 30 to 60-wt %or higher in order to optimize the interaction between the metaloxyanion precursor and substrate. The concentration can be adjusted inorder to maintain a liquid reactant mixture viscosity which enhancesatomization of the liquid reactant mixture and overall steady stateprocess and plasma conditions for conversion and yield of metal oxyanioncoated substrate. Further, the reaction zone can be run at varyingpressures including reduced pressures through higher pressures aboveatmospheric. The choice of pressure is generally a function of thecharacteristics of the metal oxyanion precursor, oxy precursor and anionforming precursor. It is preferred to maintain such conditions ofpressure which improve the overall conversion and yield of metaloxyanion coating on the substrate while reducing and/or minimizing thereaction of metal oxyanion precursor to metal oxyanion off of thesubstrate.

The feed rates of the liquid slurries and powders in general are afunction of the reaction zone design and size. In general for smallscale reaction zone designs a feed rate of from 100 grams to 500 gramsper hour can be used, whereas for larger scale, a feed rate of from 0.5Kg to 50 Kg per hour can be used.

The liquid slurries and flowable powder reactant mixtures can containvarious substantially nondeleterious materials including solvents, i.e.organonitrogen containing solvents for liquid slurries and organicpolymeric binders which may decrease or increase the elevatedtemperature or enthalpy in the reaction zone. The thermal contributionof these materials is used in order to design the thermal profile in thereaction zone in order to maximize steady state process conditions andconversion and yields of metal oxyanion coated substrate. Further, theuse of such materials, particularly, organic materials can be used toadjust the composition of the plasma gases as a function of the gascomposition from gas entry to exit from the reaction zone. For example,the hydrogen requirement for a given reaction of metal oxyanionprecursor to metal oxyanion coating can be adjusted such that a portionof the plasma and gas composition exiting the tail of the plasma can bein an overall reducing environment. The process flexibility in theintroduction of varying gases of varying characteristics allows suchchanges in gas composition as a function of plasma profile and exitgases to be made. For example, in the use of partial oxide and metalchloride precursors it has been found that a staged reducing environmentcan enhance overall conductivity of a metal oxyanion film on asubstrate. Further, the use of carbon dioxide such as in very low oxygencontaining gases from partial combustion of hydrocarbon can be usedadvantageously to promote the formation of a multiple reduction zoneswithin the reaction zones and/or a reduction zone following the exit ofthe plasma gas from the reaction zone. Further, it is possible to addauxiliary gases such as reducing gases into the plasma at differentintroduction points within the plasma.

The metal oxyanion coated substrates exit the reaction zone and arerapidly quenched to lower temperatures including temperatures whereinrelatively low, preferably no significant chemical change is takingplace of the metal oxyanion coating. The metal oxyanion coatedsubstrates are recovered by conventional means such as typical powderparticle collection means. As set forth above, the metal oxyanion coatedsubstrates can be further processed such as by annealing to furtherdensify the metal oxyanion coatings and/or more fully develop theoptimum crystal structure for enhancing overall conductivity and/orabsorbing of the final coated substrate.

As set forth above, the thermal source can be obtained from combustionsuch as a flame produced by the combustion of a gas such as acetylene,methane or low molecular weight hydrocarbons, hydrogen and ammonia. Thethermal and kinetic energy associated with the combustion process can bevaried to provide elevated temperatures and residence times and/orparticle substrate velocity within the ranges as set forth above atnon-stoichiometric flame or reducing gas conditions. The combustionflame process provides a reaction zone wherein the gas compositionwithin the reaction zone can be varied according to the gas combustioncharacteristics used to provide the reaction zone. Further, thecomposition of the gas can be varied according to the type of gas usedin the combustion process and the ratio of combustion gas to inert gasthat is used to produce a reducing flame. Thus the amount of residualoxygen, carbon dioxide and water vapor can be limited by varying thestoichiometry of the reactants, the type of fuel source and reducingconditions. Further, auxiliary gases can be added to moderate and modifythe combustion flame characteristics. In addition, such auxiliary gasesincluding inert gases can be added directly into the combustion flame oras a sheath, i.e. curtain or shroud, surrounding the combustion flame.Further, the reactant mixture can be introduced directly into thecombustion flame or as in the case of the RF induction plasma at varyingangles to the flame or on the outer or adjacent surface or tail of theflame. The temperature profiles within the combustion flame aretypically lower than the temperatures that can be achieved in the RFinduction plasma typically in the range of from about 750° K to about1,500° K. The unexpected process improvement for producing metaloxyanion coated substrates with the combustion process is the formationof a reaction zone at temperatures and residence times which allow forthe conversion of the metal oxyanion precursor on the substrate to thecoating. The various embodiments set forth above with respect toreaction mixture introduction into the reaction zone, preference foratomization of the reaction mixtures, variations on introduction of thereaction mixtures at various locations within the reaction zone or atthe tail end of the reaction zone, variations in gas composition such asreducing zones are applicable to the combustion processes.

The thickness of the metal oxyanion-containing coating can vary over awide range and optimized for a given application and is generally in therange of from about 0.01 to about 0.75 microns or even from about 0.01to about 0.5 microns, more preferably from about 0.02 microns to about0.25 microns, still more preferably from about 0.02 microns to about 0.1micron.

The reactant mixture may also include one or more other materials, e.g.,dopants, catalysts, grain growth inhibitors, binders, solvents, etc.,which do not substantially adversely affect the properties of the finalproduct, such as by leaving a detrimental residue or contaminant in thefinal product after formation of the metal oxyanion containing coating.Thus, it has been found to be important, e.g., to obtaining a metaloxyanion coating with good structural, mechanical and/or electronicand/or magnetic properties, that undue deleterious contamination of thecoating be avoided. Examples of useful other materials include organiccomponents such as organic nitrogen solvents, such as acetonitrile,dichloro acetonitrile, pyridene, chloropyridene pyrrole and mixturesthereof; certain halogenated hydrocarbons, particularly chloro andmixtures thereof. Certain of these other materials may often beconsidered as a carrier, e.g., solvent, and/or anion forming precursorfor the metal oxyanion precursor to be associated with the substrate toform the reactant mixture.

The metal oxyanion coatings are typically derived from transition metalprecursors, which contain transition elements and Group III and Group IVmetals. Examples of such metals are boron, aluminum, silica, tin,nickel, chromium, tungsten, titanium, molybdenum and zirconium. Thepreferred elements are aluminum, boron, silica, tungsten, titanium,molybdenum and zirconium.

As set forth above the metal oxyanion precursor is preferably selectedfrom the group consisting of one or more metal chlorides, metal partialoxides, oxides, organic complexes and organic salts. Further, it ispreferred that metal chlorides, organic complexes and salts and oxidesdo not allow substantially deleterious residual oxygen to remain in thecoating under the conditions of conversion to metal oxyanion in thereaction zone. Particularly preferred metal oxyanion precursors aremetal chlorides and lower valence organic nitrogen complexes.

Typical examples of metal chloride precursors are nickel chloride,lanthanum chloride, zirconium chloride, aluminum chloride, ferricchloride, tungsten pentachloride, tungsten hexa chloride, molybdenumpentachloride, indium dichloride, indium monochloride, chromium²chloride and titanium tetrachloride. Preferred metal complexes arepolyfunctional nitrogen complexes wherein such functionality is capableof complexing with the metal. Typical examples of oxides are silica,boron oxide and boric acid.

Typical examples of anion forming precursors that produce borides areboron trichloride, borazine, diborane, and triethoxy boron; that producenitrides are nitrogen and ammonia; that produce silicides are silanesand hydrosilicides; that produce carbides are methane, powdered carbon,low molecular weight halogenated hydrocarbons particularly chlorohydrocarbons, ethane and propane and that produce sulfides are hydrogensulfide and sulfur halides. In the practice of this invention, the anionforming precursor is selected for the final metal oxyanion coating to beobtained, and anions not desired in the final coating should be avoidedin the reactants and in the reaction zone.

As set forth above the oxy precursor can be derived from the metaloxyanion precursor, the anion forming precursor or from a separatecompound such as oxygen. Further the oxy precursor can be derived fromthe decomposition of various types of oxide materials in the reactionzone including nitrous oxide, water and other similar componentspreferably gaseous components that provide the oxygen component for themetal oxyanion products of this invention.

The particular preferred coatings are silicon oxynitride, oxycarbide andoxyboride, aluminum oxynitride, zirconium oxycarbide and oxysilicide,tungsten oxysulfide, boron oxycarbide and oxynitride, titaniumoxyboride, oxycarbide, oxycarbonitride, oxysilicide and oxynitride,molybdenum oxysilicide and oxysulfide and iron oxysilicide andoxynitride.

As set forth above, it has been found that the substrate can becontacted with a metal oxyanion precursor to form a flowable powderreactant mixture. For example, a metal oxyanion precursor can be appliedto the substrate as a powder, a precipitate and/or as a liquid filmparticularly at a thickness of from about 0.05 to about 1 micron, thethickness in part being a function of the substrate particle size, i.e.smaller substrate particles generally require even smaller sizeprecursors and thicknesses. The precursor can be applied dry to a drysubstrate and as a charged fluidized precursor, in particular having acharge opposite that of the substrate or at a temperature where theprecursor contacts and adheres to the substrate. In carrying out theprecursor coating, a coating system can be, for example, one or moreelectrostatic fluidized beds, spray systems having a fluidized chamber,and other means for applying for example powder, preferably in a filmforming amount. The amount of precursor used is generally based on thethickness of the desired metal oxyanion coating and incidental lossesthat may occur during processing. The process together with conversionto a metal oxyanion containing coating can be repeated to achievedesired coating properties, such as desired gradient conductivities.

Typically, the fluidizing gaseous medium is selected to be compatiblewith the metal oxyanion precursor powder, i.e., to not substantiallyadversely affect the formation of a metal oxyanion coating on thesubstrate during conversion to a metal oxyanion-containing film.

Generally, gases such as nitrogen, argon, helium and the like, can beused, with nitrogen being a gas of choice, where no substantial adversereaction of the precursor takes place prior to the reaction to the metaloxyanion coating. The gas flow rate for powder coating is typicallyselected to obtain fluidization and charge transfer to the powder. Finepowders require less gas flow for equivalent deposition. It has beenfound that very small amounts of water vapor can enhance chargetransfer. The temperature for contacting the substrate with a precursoris generally in the range of about 0° C. to about 100° C. or higher,more preferably about 20° C. to about 40° C., and still more preferablyabout ambient temperature. The substrate however, can be at temperaturesthe same as, higher or substantially higher than the powder.

The time for contacting the substrate with precursor is generally afunction of the substrate bulk density, thickness, precursor size andgas flow rate. The particular coating means is selected in partaccording to the above criteria, particularly the geometry of thesubstrate. For example, particles, spheres, flakes, short fibers andother similar substrate, can be coated directly in a fluidized bedthemselves with such substrates being in a fluidized motion or state.Typical contacting time can vary from seconds to minutes, preferably inthe range of about 1 second to about 120 seconds, more preferably about2 seconds to about 30 seconds.

Typical metal oxyanion precursor used for flowable reaction mixtures arethose that are powder reaction mixtures at pre reaction zone conditionsand can be liquidous or solid at the fast reaction process conditions atthe elevated temperatures in the reaction zone. It is preferred that theprecursor at least partially melt and substantially wet the surface ofthe substrate, preferably having a low contact angle formed by theliquid precursor in contact with the substrate and has a relatively lowvapor pressure at the fast reaction and temperature conditions,preferably melting within the range of about 100° C. to about 650° C. orhigher. As set forth above, the fast reaction process conditions canallow for the metal oxyanion precursor to rapidly react with the oxyprecursor and anion forming precursor to a highly viscous and/orintermediate solid prior to substantial conversion to the metal oxyanioncoating. The process conditions can allow for the association of thisintermediate metal oxyanion component to form and reduce thevolatilization and/or less of the metal oxyanion precursor off of thesubstrate.

As set forth above, the metal oxyanion precursors are preferablypreassociated with the substrate and gas fluidized into the reactionzone. It has been found that the preassociation of a thin coating ofmetal oxyanion precursor becomes highly reactive in the reaction zonethereby reducing and/or minimizing the loss of metal oxyanion precursorthrough volatilization. Examples of such association of metal oxyanionprecursor are fine powder coating of the substrate, precipitation of themetal oxyanion precursor on the substrate followed by drying such asspray drying, the formation of a liquid film on the flowable powdersubstrate such as by liquid droplets and conventional spray and dipcoating processes for preparing dry films on powder substrates. Thus,for example an organic metal oxyanion precursor such as a titanate, asilane and/or other organic metal derivatives can be sprayed on thepowder substrate and dried and/or contacted through the use of anaqueous medium followed by drying such as spray drying.

As set forth above, the metal oxyanion precursor can be associated withthe substrate as a liquid slurry. For example, a liquid soluble metalchloride, i.e. chloride salt or a suspension and/or precipitatedsuspension, may be used. The use of liquid metal oxyanion precursorprovides advantageous substrate association particularly efficient anduniform association with the substrate. In addition, coating materiallosses are reduced.

The metal oxyanion precursors set forth above with respect to flowablepowders in general can be used also to make the liquid slurries. Inaddition, liquids, low melting and liquid soluble metal salts can beused advantageously for the liquid slurries.

As set forth above, it is preferred that the reaction mixture liquidslurries maximize the concentration of the substrate consistent withslurry viscosity and atomization requirements in the reaction zone. Theamount of metal oxyanion precursor which is incorporated into the slurryis generally a function of the thickness of the metal oxyanion coatingon the substrate for the final product. For example, a metal oxyanioncoating of 50 nanometers will typically require less than a 150nanometer metal oxyanion precursor coating. Further, the surface area ofthe substrate, typically a function of particle size per unit weightwill effect the concentration of the metal oxyanion precursor. Thereactant slurries can contain a solvent which allows for thesolubilization and/or precipitation of the metal oxyanion precursor. Thepreferred solvents are organic heteroatom solvent systems which allowfor solubilization of the metal oxyanion precursor and which do notcontribute substantially deleterious anions to the desired coating. Forexample, a preferred liquid slurry which contains soluble metal oxyanionprecursor is titanium tetrachloride. The liquid slurries in addition canhave a pH higher or less than 7 which enhances overall solubility and/orprecipitation.

The precipitated liquid slurry reaction mixtures can be made by forminga first soluble solution of an appropriate metal oxyanion precursor suchas metal chloride salts in a solution such as a basic solution andadding such solutions slowly at elevated temperature such as from about50° to 90° C. to a suspension of the substrate. The gradual addition ofthe metal oxyanion precursor solution generally in the presence of smallamounts of hydroxyl ion in the substrate suspension provides for a slowand gradual partial hydrolysis and precipitation of the salts,preferably on the surfaces of the substrate in a uniform layer. Theprecipitant slurry reactant mixture is introduced into the reaction zonefor conversion to the metal oxyanion coated substrate. One of thesignificant advantages of the process of this invention usingprecipitant slurry reaction mixtures is that the slurry itself can bedirectly fed into the reaction zone without requiring separation of theprecipitant plus substrate, washing of the substrate and drying of theprecipitant associated substrate. The precipitant slurry reactionmixture and the precipitant process are typically undertaken at highsubstrate liquid slurry concentrations without the introduction ofdeleterious contaminants. Thus it is preferred to use solvent systemswhich do not contribute deleterious contaminants to the metal oxyanioncoating. If a source of hydroxyl ion is used to enhance theprecipitation process it is preferred to use a source such as ammoniumhydroxide which does not substantially interfere with the finalproperties of the metal oxyanion film. Further, in the case ofprecipitant reaction mixtures, the precipitant substrates can befiltered, washed of extraneous ions and reslurried for use as a reactionmixture. In order to control the viscosity of the liquid slurries,particularly at high substrate concentration a dispersant or defloculantcan be added to reduce and/or minimize any substrate agglomeration.

The metal oxyanion precursor to be contacted with the substrate may bepresent in an atomized state. As used in this context, the term“atomized state” refers to both a substantially gaseous state and astate in which the metal oxyanion precursor is present as drops ordroplets and/or solid dispersion such as colloidal dispersion in forexample a carrier gas, i.e., an atomized state. Liquid state metaloxyanion precursors may be utilized to generate such reaction mixture.

Any suitable means can be utilized to produce “the atomized state.” Aparticularly preferred atomized state is drops or droplets particularlyas a droplet dispersion. Typical examples of droplet and/or aerosolgenerators include nozzles and ultrasonic atomizing nozzles. Aparticularly preferred atomization technique is an ultrasonic atomizingnozzle since the nozzle produces a soft, low velocity spray, typicallyin the order of three to five inches per second. Further, droplet sizescan be varied over a wide range depending on the particle sizedistribution of the substrate. A particularly preferred ultrasonicatomizing nozzle is manufactured by Sono-Tek Inc. such as model8700-120. In a preferred process the ultrasonic generator produces afine mist having an average droplet size of about 18 microns or less.The droplets are contacted with a carrier gas, typically an inertcontaining gas such as argon or a reactive anion forming precursor gas.In a preferred embodiment the carrier gas contains the dispersedsubstrate which allows for substrate and droplet association. Thecontacting between the carrier gas dispersed substrate and the dropletsallow for a film forming amount of the droplets to become associatedwith at least a portion of the surfaces of the substrates. The substrateand droplets are typically maintained in a carrier gas fluidizedcondition which allows for association of the droplets with thesubstrates. Typically the contacting between the carrier gas substrateand droplets is at ambient temperature and for a period of time to allowfor the association of the droplets on the substrate surfaces. In orderto enhance contacting efficiencies a suitable apparatus such as a staticmixer can be used to accelerate the droplet substrate association. Thecontacting time between the carrier gas substrate and droplets under thecarrier gas fluidized conditions is typically less than twenty seconds,more typically less than ten seconds. In a preferred embodiment thedroplet associated substrate in a fluidized carrier gas is contacted atfast reaction and elevated temperature reducing conditions in a reactionzone in the presence of an oxy precursor and anion forming precursor asset forth above. In a preferred embodiment the start of contacting underfast reaction conditions in the reaction zone is proximate in time tothe association of the droplets with the substrate, typically at asubstrate film reaction time after such substrate association of lessthan five seconds, more typically less than two seconds.

In a further preferred embodiment the metal oxyanion forming compound iscombined to form a liquid mixture prior to droplet formation. Thisallows for the metal oxyanion forming compound to be intimatelyassociated with the surfaces of the substrates. Further it is preferredthat the metal oxyanion forming compound has a higher reaction rate inthe reaction zone to metal oxyanion coating than the overall evaporationrate of the metal oxyanion forming compound. Thus, metal oxyanionforming compounds having boiling point above 100° C., more preferablyabove 150° C. at atmospheric pressure are preferred.

In addition to the other materials, as noted above, the reactant mixturemay also include one or more grain growth inhibitor components. Suchinhibitor component or components are present in an amount effective toinhibit grain growth in the metal oxyanion containing coating. Reducinggrain growth leads to beneficial coating properties, e.g., higherconductivity, more uniform morphology, and/or greater overall stability.Among useful grain growth inhibitor components are components whichinclude at least one metal ion, in particular potassium, calcium,magnesium, silicon, zinc and mixtures thereof. These components aretypically used at a concentration in the final coating of from about0.01 to 1.0 wt % basis coating. Of course, such grain growth inhibitorcomponents should have no substantial detrimental effect on the finalproduct.

The anion forming precursor may be deposited on the substrate separatelyfrom the metal oxyanion precursor, for example, before and/or during themetal oxyanion precursor/substrate contacting. If the anion formingprecursor component is deposited on the substrate separately from themetal oxyanion precursor it should be deposited after the metal oxyanionprecursor but before reaction to the metal oxyanion film.

Any suitable anion forming precursor may be employed in the presentprocess and should provide sufficient anion forming precursor so thatthe final metal oxyanion coating has the desired properties, e.g.,conductivity, stability, absorption properties, etc. Care should beexercised in choosing the anion forming precursor. For example, theanion forming precursor should be sufficiently compatible with, forexample, the metal oxyanion precursor so that the desired metal oxyanioncoating can be formed. Anion forming precursors which are excessivelyvolatile (relative to the metal oxyanion precursor), at the conditionsemployed in the present process, can be used since, for example, thefinal coating can be sufficiently developed with the desired propertieseven though an amount of the anion forming precursor may be lost duringprocessing. It may be useful to include one or more property alteringcomponents, e.g., boiling point depressants, in the reaction mixture.When used, such property altering component or components are includedin an amount effective to alter one or more properties, e.g., boilingpoint, of the precursor, e.g., to improve the compatibility or reducethe incompatibility between the precursors.

As set forth above, the reaction zone gas phase constituents aretypically adjusted to provide either a reducing or oxygen environmentwithin the reaction zone, such as preferably with hydrogen or oxygen.Further, reducing conditions can be further enhanced at the tail end ofthe zone as the metal oxyanion coated particle substrates undergoreaction quench at significantly lower temperatures. The use of thecombination of staged reduction zones within the reaction zone and tailportion of the reaction zone can be particularly beneficial for creatingoptimum properties, i.e. film uniformity, morphology and oxyanionstoichiometry without substantial deleterious oxide content.

In addition to stage reduction, the anion forming precursor when in theform of a gas can be staged for optimizing the contact efficiency withthe metal oxyanion precursor coated powder substrate in the reactionzone. Further, the gaseous constituents in the reaction zoneparticularly under reducing conditions should be present at aconcentration that enhances reduction of oxide type metal oxyanionprecursors and/or contaminant oxygen that might enter the reaction zone.As set forth above, the metal oxyanion coating on the substrate shouldnot have substantially deleterious contaminants such as the deleteriouspresence of contaminant amounts of metals and contaminant oxygen anion.

The liquid compositions, which include metal oxyanion precursor, canalso include the anion forming precursor. In this embodiment, the anionforming precursor can be soluble and/or dispersed homogeneously and/oratomizeable as part of the reactant mixture. Such mixtures areparticularly effective since the amount of anion forming precursor inthe final metal oxyanion coating can be controlled by controlling theconcentration of anion forming precursor in the reactant mixture. Inaddition, both the oxyanion precursor and anion forming precursor areassociated with the substrate in one step.

The powder substrate preferably is composed of at least a part of anysuitable inorganic material and may be in any suitable form. By the termsuitable inorganic substrate is meant that the majority of the externalsurface of the particle substrate be inorganic, more preferably greaterthan about 75% and still more preferably greater than about 95% of thesurface being inorganic. The internal core of the particle substratescan be organic, preferably organic polymers having high temperaturethermal stability under the fast reaction temperature conditions in thereaction zone. The polymers can be thermoplastics or thermosets,preferably high temperature thermoplastics such as polyimides,polyamide-imides, polyetherimides, bismalemides, fluoroplastics such aspolytetrafluoroethylene, ketone-based resins, polyphenylene sulfide,polybenzimidazole, aromatic polyesters, and liquid crystal polymers.Most preferred are imidized aromatic polyimide polymers,para-oxybenzoylhomopolyester and poly(para-oxybenzoylmethyl) ester. Inaddition polyolefines, particularly crystalline high molecular weighttypes can be used. The preferred organic substrates are high temperaturestable substrates, preferably inorganic organic substrates prepared byprecoating the organic substrate with an inorganic precoat as set forthbelow.

Preferably, the substrate is such so as to minimize or substantiallyeliminate deleterious substrate, coating reactions and/or the migrationof ions and other species, if any, from the substrate to the metaloxyanion-containing coating which are deleterious to the functioning orperformance of the coated substrate in a particular application.However, a controlled substrate reaction which provides the requisitestoichiometry can be used and such process is within the scope of thisinvention. In addition, the substrate can be precoated to minimize ionmigration, for example an alumina and/or a silica including a silicateprecoat and/or to improve wetability and uniform distribution of thecoating materials on the substrate and/or to provide a surface forreaction with the anion forming precursor. The precoats can comprise oneor more members of a group of alumina, zirconium, silica, tungsten andtitanium oxides and other oxide halides and organooxy halides. Theprecoats can be deposited on the substrates including inorganic andorganic core substrates using any suitable technique such as hydrolysisand precipitation of a soluble salt. Further, as set forth above, theprecoats can be deposited on the substrates using such techniques asspray coating, dip coating followed by drying such as spray drying. Inaddition, the precoat process can be repeated in order to obtain aprecoat thickness to for example minimize deleterious effects fromcations contained in the substrate and/or improve the thermal barrierproperties of the precoat in relationship to an organic core and/or toprovide the desired metal oxyanion coating thickness.

In addition to the above techniques for forming a precoat, the substrateparticles, particularly the inorganic particles, can be processed inaccordance with the process of this invention with a precoat formingmaterial such as silicic acid or disilicic acid. In general, the precoatprecursor would be combined with the substrate to form a precoatreaction mixture which is then subjected to process conditions in thereaction zone in order to obtain reaction of the precursor precoatcomponent on the substrate. It is contemplated within the scope of thisinvention that a single or multi step process can be used, i.e. thefirst stage of a multistage being a precoat of the substrate in thereaction zone using the various types of feeds similar to those setforth above which contain the precoat precursor and subjecting such feedto fast reaction elevated temperature conditions in a reaction zone toform the precoated substrate. The precoated substrate can be combinedwith the metal oxyanion precursor to be further processed according tothe process of this invention.

It has also been found that the substrate itself can be selectivelyreacted and/or melted at the surface to produce a reactive surfaceand/or a precoat barrier layer, preferably a melt/resolidification/metaloxyanion coating, still more preferably a majority or even greatercrystalline layer on the outer surface of the inorganic substrate. Theselective reaction and/or melting of the surface of the inorganicsubstrate can provide both the metal oxyanion coating and barrierproperties as well as enhanced bondability of the metal oxyanion coatingon the substrate, particularly with the formation of crystalline typesurface coating as set forth above. The process for the selectivereaction and/or melting of the surface of the inorganic substrate can bedone in multiple process steps or in a single step in carrying out theprocess of this invention. For example, the selective melting of theexternal surface of the inorganic substrate can be done in a mannersimilar to the formation of a reactive and/or barrier coating as setforth above followed by incorporating the surface modified substratealong with the anion forming precursor to form the reactant mixture. Thereaction mixture is then processed according to the process of thisinvention. In addition the reactant mixture can be introduced into thereaction zone under conditions wherein the selective reaction and/ormelting and resolidification of the surface of the inorganic substratetakes place, i.e. a single step process in the presence of an anionforming precursor. It has been found that the inorganic substrate havinga surface that has undergone selective reaction and/or melting,resolidification has unique properties with the inner core associatedwith the metal oxyanion coating. These improved properties can includeenhanced coating and barrier properties, bonding of the inner core withthe metal oxyanion coating and overall morphology stability.

In order to provide for controlled conductivity and/or absorption ofmetal oxyanion coatings, it is preferred that the substrate and/or innercore be substantially non-conductive and/or non-deleterious furtherreactive and/or substantially non-absorbing when the coated substrate isto be used as a component/such as additive in an electronic device,packaging device and/or film device. The substrate can be partially orcompletely inorganic, for example mineral, glass, ceramic and/or carbon.Examples of three dimensional substrates which can be coated using thepresent process include spheres, extrudates, flakes, fibers, aggregates,porous substrates, stars, irregularly shaped particles, tubes, such ashaving an average largest dimension of from about 0.05 microns to about250 microns, more preferably from about 1 micron to about 75 microns.

A particularly unique embodiment of the present metal oxyanion coatedparticles is the ability to design a particular density for a substratethrough the use of one or more open or closed cells, including micro andmacro pores particularly, including cell voids in spheres which spheresare hereinafter referred to as hollow spheres. Thus such densities canbe designed to be compatible and synergistic with other components usedin a given application, particularly optimized for compatibility inliquid systems such as polymer film coating and composite compositions.The average particle density can vary over a wide range such asdensities of from about 0.1 g/cc to about 2.00 g/cc, more preferablyfrom about 0.13 g/cc to about 1.5 g/cc, and still more preferably fromabout 0.15 g/cc to about 0.80 g/cc.

A further unique embodiment of the present invention is the ability toselectively have a metal oxyanion coating on the outer surface areawhile limiting the metal oxyanion coating on the internal pore surfacearea of the substrate typically limiting the coating to at least about10% noncoated internal pore surface area as a percentage of the totalsurface area of the substrate. Typically, the porous substrates willhave a total surface area in the range of from about 0.01 to about 700m²/gram of substrate, more typically from about 1 to about 100 m²/gramof substrate. Depending on the application such as for catalysts, thesurface area may vary from about 10 to about 600 m²/gram of substrate.

As set forth above, porous powder substrate particles can be in manyforms and shapes, especially shapes which are not flat surfaces, i.e.,non line-of-site materials such as pellets, fiber like, beads, includingspheres, flakes, aggregates, and the like. The percent apparentporosity, i.e., the volume of open pores expressed as a percentage ofthe external volume can vary over a wide range and in general, can varyfrom about 20% to about 92%, more preferably, from about 40% to about90%. A particularly unique porous substrate is diatomite, a sedimentaryrock composed of skeletal remains of single cell aquatic plants calleddiatoms typically comprising a major amount of silica. Diatoms areunicellular plants of microscopic size. There are many varieties thatlive in both fresh water and salt water. The diatom extracts amorphoussilica from the water building for itself what amounts to a strong shellwith highly symmetrical perforations. Typically the cell walls exhibitlacework patterns of chambers and partitions, plates and apertures ofgreat variety and complexity offering a wide selection of shapes. Sincethe total thickness of the cell wall is in the micron range, it resultsin an internal structure that is highly porous on a microscopic scale.

Further, the actual solid portion of the substrate occupies only fromabout 10-30% of the apparent volume leaving a highly porous material foraccess to liquid. The mean pore size diameter can vary over a wide rangeand includes macroporosity of from about 0.075 microns to 10 micronswith typical micron size ranges being from about 0.5 microns to about7.5 microns. As set forth above, the diatomite is generally amorphousand can develop crystalline character during calcination treatment ofthe diatomite. For purposes of this invention, diatomite as produced orafter subject to treatment such as calcination are included within theterm diatomite.

The particularly preferred macroporous particles for use in thisinvention are diatomites obtained from fresh water and which havefiber-like type geometry. By the term fiber-like type geometry is meantthat the length of the diatomite is greater than the diameter of thediatomite and in view appears to be generally cylindrical and/orfiberlike. It has been found that these fiber-like fresh waterdiatomites provide improved properties in coatings and compositeapplications.

As set forth above, substrates can be inorganic for example, carbonincluding graphite and/or an inorganic oxide. Typical examples ofinorganic oxides which are useful as substrates include for example,substrates containing one or more silicate, aluminosilicate, silicaparticularly high purity silica, sodium borosilicate, insoluble glass,soda lime glass, soda lime borosilicate glass, silica alumina, titaniumdioxide, mica, as well other such glasses, ceramics and minerals whichare modified with, for example, another oxide such as titanium dioxideand/or small amounts of iron oxide.

Additional examples of substrates are wollastonite, titanates, such aspotassium hexa and octa titanate, carbonates and sulfates of calcium andbarium; borates such as boric oxide, boric acid and aluminum borate, anatural occurring quartz and various inorganic silicates, clays,pyrophyllite and other related silicates.

A particularly unique metal oxyanion coated three-dimensional substrateis a flake and/or fiber particle, such as having an average largestdimension, i.e. length of from about 0.1 micron to about 200 micronsmore preferably from about 1 micron to about 100 microns, and still morepreferably from about 5 microns to about 75 microns, particularlywherein the aspect ratio, i.e., the average particle length divided bythe thickness of the particle is from about five to one to about 200 to1, more preferably from about 25 to 1 to about 200 to 1 and still morepreferably, from about 50 to 1 to about 200 to 1. Generally, theparticles will have a thickness varying from about 0.1 microns to about15 microns, more preferably from about 0.1 micron to about 10 microns.The average length, i.e., the average of the average length plus averagewidth of the particle, i.e., flake, will generally be within the aspectratios as set forth above for a given thickness. Thus for example theaverage length as defined above can vary from about 1 micron to about300 microns, more typically from about 20 microns to about 150 microns.In general, the average length can vary according to the type ofsubstrate and the method used to produce the platelet material. Forexample, C glass in general has an average length which can vary fromabout 20 microns up to about 300 microns, typical thicknesses of fromabout 1.5 to about 15 microns. Other particle materials for example,hydrous aluminum silicate mica, in general can vary in length from about5 to about 100 microns at typical thicknesses or from about 0.1 to about7.0 microns, preferably within the aspect ratios set forth above. Inpractice the particles which are preferred for use in such applicationsin general have an average length less than about 300 microns and anaverage thickness of from about 0.1 to about 15 microns. Ceramic fibersare particularly useful substrates.

A particular unique advance in new products resulting from the processof this invention are the production of metal oxyanion coated nanoparticle substrates typically having an average particle size less than3,000 nanometers, typically less than 2000 and still typically less than1000 nanometers. In many applications the average particle size will beless than about 200 nanometers. The particle size distribution of thenano particle substrates are skewed towards the smaller particle sizeand typically have greater than 90%, often greater than 95% of the totalnumber particles on a weight basis, less than 3,000 nanometers,typically less than 2000 nanometers, and still more typically less than1000 nanometers. It has been discovered that the use of liquid slurryreaction mixtures particularly metal oxyanion precursor which aresoluble in the slurry liquid are able to produce metal oxyanion coatednanosubstrates which vary in thickness from about 2% to about 75%, morepreferably from about 5% to about 60% of the average thickness on thesmallest dimension of the substrate particle, such as the thickness in aflake or the diameter in a fiber. The various physical and chemicalproperties of the substrates and coatings as set forth above areapplicable to nanosubstrates. The significant advantage of the solublemetal oxyanion precursor is the ability to provide the concentration ofthese coating forming components that produce the desired coatingthickness on the nanosubstrates.

A particular unique substrate is referred to as swelling clays orsmectites. These types of clays have a layered structure where in eachlayer can be treated to expand the spacing between layers such as toprovide individual layers of the clay of vary small thicknesses such asfrom about 1 to 2 nanometers. The aspect ratios are significantparticularly if the largest length extends to 1,000 nanometers. Thespacing between the different sheets are called the gallery which areexpanded upon treatment particularly with polar materials to provide forincreased spacing between each sheet.

These phyllosilicates, such as smectite clays, e.g., sodiummontmorillonite and calcium montmorillonite, can be treated with polarmolecules, such as ammonium ions, to intercalate the molecules betweenadjacent, planar silicate layers, for intercalation of precursor betweenthe layers, thereby substantially increasing the interlayer(interlaminar) spacing between the adjacent silicate layers. Thethus-treated, interclalted phyllosilicates, having interlayer spacingsof at least about 10-20. ANG. and up to about 100 .ANG., then can beexfoliated, e.g., the silicate layers are separated, e.g., mechanically,by high shear mixing. The individual layers have been found tosubstantially improve one or more properties of polymer coatings andcomposites, such as mechanical strength and/or high temperaturecharacteristics.

Useful swellable layered materials include phyllosilicates, such assmectite clay minerals, e.g., montmorillonite, particularly sodiummontmorillonite; magnesium montmorillonite and/or calciummontmorillonite; nontronite; beidellite; volkonskoite; hectorite;saponite; sauconite; sobockite; stevensite; svinfordite; vermiculite;and the like. Other useful layered materials include micaceous minerals,such as illite and mixed layered illite/smectite minerals, such asrectorite, tarosiovite, ledikite and admixtures of illites with the clayminerals set forth above.

As set forth above the reaction mixture can be in a flowable powder formwith the metal oxyanion precursor present on the surface of thesubstrate as has been illustrated above. The metal oxyanion precursorcan be associated with the surface of the substrate by attractionthrough opposite static charges. In addition a binder can be associatedwith the metal oxyanion precursor, which enhances the association of theprecursor with the substrate. The binder can be inorganic or organic. Asset forth above, the binder should not introduce any substantialdeleterious contaminants into the metal oxyanion coating orsubstantially adversely affect the overall film properties such asconductive or absorption properties. The binders can be for examplepolymeric type such as polyvinylalcohol or polyvinylpyrrolidone. Inaddition, the binder can have both organic and inorganic functionalitysuch as an organic silicate such as an ethyl silicate. In addition, theinorganic binders can be used such as calcium silicate, boric oxide andcertain carbonate, nitrates and oxalates. In the case of organic bindersit is preferred to use such organic binders that will be converted to acarbon oxide such as carbon monoxide or carbon dioxide under the processconditions in the reaction zone without leaving any substantialdeleterious carbon or oxygen contaminant associated with the metaloxyanion coated substrate. In addition, the use of organic binders canprovide for a reducing atmosphere in the reactor zone or the exit of thereactor zone. It is preferred to use a binderless flowable powderreaction mixture in order to eliminate potential contaminant effects.When a binder is used, the concentration of the binder is such as tomaintain the individual particle substrate integrity or if agglomerationdoes occur, to be easily converted to nonagglomerated particles throughlow severity mechanical processing such as ball milling.

The coated particles are particularly useful in a number ofapplications, particularly conductivity and absorption type applicationssuch as catalysts, thermal dissipation elements, electrostaticdissipation elements, electromagnetic interference shielding elements,electrostatic bleed elements, protective coatings and the like.

In practice spherical particles for use in applications in general havea roundness associated with such particles, generally greater than about70% still more preferably, greater than about 85% and still morepreferably, greater than about 95%. The spherical products offerparticular advantages in many of such applications disclosed herein,including enhanced dispersion and rheology, particularly in variouscompositions such as polymer compositions, coating compositions, variousother liquid and solid type compositions and systems for producingvarious products such as coatings and polymer composites. Typicalexamples of products are boron oxynitride, silicon oxycarbide andoxynitride, iron oxysilicide, titanium oxycarbide, boride andoxysilicide, aluminum oxynitride and molybdenum oxysilicide

Any suitable matrix material or materials may be used in a compositewith the metal oxyanion coated substrate. Preferably, the matrixmaterial comprises a polymeric material, e.g., one or more syntheticpolymers, more preferably an organic polymeric material. The polymericmaterial may be either a thermoplastic material or a thermoset material.Among the thermoplastics useful in the present invention are thepolyolefins, such as polyethylene, polypropylene, polymethylpentene andmixtures thereof; and poly vinyl polymers, such as polystyrene,polyvinylidene difluoride, combinations of polyphenylene oxyanion andpolystyrene, and mixtures thereof. Among the thermoset polymers usefulfor powders of the present invention are epoxies, phenol-formaldehydepolymers, polyesters, polyvinyl esters, polyurethanes,melamine-formaldehyde polymers, and urea-formaldehyde polymers.

In addition, a thermal and/or electrostatic dissipation/electromagneticinterference shielding element is provided which comprises a threedimensional substrate, e.g., an inorganic substrate, having a conductivemetal oxyanion-containing coating on at least a portion of all threedimensions thereof. The coated substrate is adapted and structured toprovide at least one of the following; thermal and/or electrostaticdissipation and/or bleed and electromagnetic interference shielding.

A very useful application for the products of this invention is forstatic, for example, electrostatic, dissipation and shielding,particularly for polymeric parts, and more particularly as a means foreffecting static dissipation including controlled static discharge anddissipation such as used in certain electro static painting processesand/or electric field absorption in parts, such as parts made ofpolymers and the like, as described herein. Certain of the presentproducts can be incorporated directly into the polymer or a carrier suchas a cured or uncured polymer based carrier or other liquid, as forexample in the form of a liquid, paste, hot melt, film and the like.These product/carrier based materials can be directly applied to partsto be treated to improve overall performance effectiveness. A heatingcycle is generally used to provide for product bonding to the parts. Aparticularly unexpected advantage is the improved mechanical properties,especially compared to metallic additives which may compromisemechanical properties. In addition, the products of this invention canbe used in molding processes to allow for enhanced static dissipationand/or shielding properties of polymeric resins relative to an articleor device or part without such product or products, and/or to have apreferential distribution of the product or products at the surface ofthe part for greater volume effectiveness within the part.

The particular form of the products, i.e., fibers, flakes, irregularlyshaped and/or porous particles, or the like, is chosen based upon theparticular requirements of the part and its application, with one ormore of flakes, fibers and particles, including spheres, being preferredfor polymeric parts. In general, it is preferred that the products ofthe invention have a largest dimension, for example, the length of fiberor particle or side of a flake, of less than about 300 microns, morepreferably less than about 150 microns and still more preferably lessthan about 100 microns. It is preferred that the ratio of the longestdimension, for example, length, side or diameter, to the shortestdimension of the products of the present invention be in the range ofabout 500 to 1 to about 10 to 1, more preferably about 250 to 1 to about25 to 1. The concentration of such product or products in theproduct/carrier and/or mix is preferably less than about 60 weight %,more preferably less than about 40 weight %, and still more preferablyless than about 20 weight %. A particularly useful concentration is thatwhich provides the desired performance while minimizing theconcentration of product in the final article, device or part.

The products of this invention find particular advantage in staticdissipation parts, for example, parts having a surface resistivity inthe range of about 10⁴ ohms/square to about 10¹² ohms/square. Inaddition, those parts generally requiring shielding to a surfaceresistivity in the range of about 1 ohm/square to about 10⁵ ohms/squareand higher find a significant advantage for the above products due totheir mechanical properties. A further advantage for certain of theabove products is their ability to provide static dissipation and/orshielding in adverse environments such as in corrosive water and/orelectro galvanic environments. As noted above, certain products have theability to absorb electro fields. The unique ability of the products toabsorb allows parts to be designed which can minimize the amount ofreflected electro fields that is given off by the part. This latterproperty is particularly important where the reflected fields canadversely affect performance of the part.

In yet another embodiment, metal oxyanion coated substrates includingoxycarbide and oxysulfide coatings such as molyoxycarbide and zanthanumoxysulfide, and optionally at least one additional catalyst componentcan be used as catalyst supports and/or catalysts in an amount effectiveto promote the desired chemical reaction. Preferably, the additionalcatalyst component is a metal and/or a component of a metal effective topromote the chemical reaction. A particularly useful class of chemicalreactions are those involving selective chemical oxidation or reductionreactions including oxidative coupling of methane to alkanes andalkenes, hydrocarbon reforming, dehydrogenation, such as alkylaromaticsto olefins, olefins to dienes, alcohols to ketones, hydrodecyclization,isomerization, ammoxidation, such as with olefins, aldol condensationsusing aldehydes and carboxylic acids and the like. Such reactions may bepromoted using the present catalysts.

Any suitable additional catalyst component may be employed, providedthat it functions as described herein. Among the useful metal catalyticcomponents are those selected from components of tin compounds, the rareearth metals, certain other catalytic components and mixtures thereof,in particular catalysts containing gold, silver, copper, vanadium,chromium, cobalt molybdenum, tungsten, zinc, indium, the platinum groupmetals, i.e., platinum, palladium, and rhodium, iron, nickel, manganese,cesium, titanium, etc. Although metal containing compounds may beemployed, it is preferred that the metal catalyst component (and/ormetal sensing component) included with the metal oxyanion coatedsubstrates comprise elemental metal and/or metal in one or more activeoxidized forms, for example, Cr₃O₃, Ag₂O, etc.

The following examples illustrate the processes of this invention.

EXAMPLE 1

A flowable powder reaction mixture is formed from a high purity silicaplatelet having an average particle size of about 50 microns andtitanium tetrachloride by liquid film formation using ultrasonic dropletformation.

The reaction mixture is fed into a reaction zone as an ammonia, oxygengas mixture fluidized flowable powder at elevated temperature and at apreformed stoichiometry to form oxynitride. The elevated temperature of2700° K is maintained by an RF induction plasma system operating at apower of about 30 kW at a frequency of 3 MHz. The central swirl gas isargon and the sheath gas, a mixture of argon and hydrogen. The anionforming precursor carrier gas is ammonia and the oxy precursor gas isoxygen. The powder reaction mixture is introduced into the reaction zoneat a flow rate of 35 grams per minute. The gas velocities in thereaction zone are controlled to allow for an average particle residencetime of about 3.0 milliseconds. The temperature within the reaction zoneis controlled to allow for the structural solid integrity maintenance ofthe substrate. The introduction of the reaction mixture is assisted bythe gas atomization of the reaction mixture. A titanium oxynitridecoated silica powder substrate is recovered in a collection zone. Thecollection zone uses a fabric bag filter to remove and recover the metaloxyanion coated substrates.

EXAMPLE 2

Example 1 is repeated except that tetramethoxy titanium is used as themetal oxyanion precursor, no oxygen is introduced into the reaction zoneand methane is used as the anion forming precursor and part of thecarrier gas. A titanium oxycarbide coated silica substrate is recoveredin the collection chamber.

EXAMPLE 3

Example 1 is repeated except that a reducing flame combustion thermalsource is used in place of the RF induction plasma system. In place ofthe central, sheath and carrier gases, a combustion gas having minimummole % oxygen is generated using nitrogen diluted air and ammonia. Theaverage particle substrate residence time in the reaction zone was 5milliseconds. A titanium oxynitride coated silica substrate isrecovered.

EXAMPLE 4

Example 1 is repeated except that the reaction mixture is a free flowingpowder obtained from contacting the silica platelet substrate with ametal oxyanion precursor aluminum chloride. The powder reaction mixtureis introduced at a rate of about 40 grams per minute. The averagevelocity of the particle substrate is 10 meters per second. An aluminumoxynitride silica platelet is recovered.

EXAMPLE 5

Example 4 is repeated except that the aluminum chloride is replaced byzirconium oxychloride. A zirconium oxynitride coating on the silicasubstrate is recovered in the collection zone.

EXAMPLE 6

Example 2 is repeated except that the substrate is mica and the mica isprecoated with diethyl chlorosilane silica precursor in place of thetitanium precursor to form a reactive coating. The average particle sizeof the mica is 20 microns. A silicon oxycarbide coated mica is recoveredin the collection zone.

EXAMPLE 7

Example 6 is repeated except the mica is replaced with a polyimidepowder having an average particle size of 40 microns. The silaneprecursor is diethyl chlorosilane. A silicon oxycarbide coated polyimidesubstrate is recovered.

EXAMPLES 8 and 9

Examples 1 and 2 are repeated except the average particle substrateresidence time is increased to 30 milliseconds. A product having auniform crystalline coating on the silica substrate is recovered in thecollection zone.

While this invention has been described with respect to various specificexamples and embodiments, it is to be understood that the invention isnot limited thereto and that it can be variously practiced within thescope of the following claims.

What is claimed is:
 1. An article comprising a thermally associatednondeleterious contaminated metal oxyanion coated three dimensionalpowder particle substrate having an inner substrate core, a thermallyreactive surface chemically different from said core on at least a partof said inner core and a metal oxyanion coating thermally formed fromsaid reactive surface, said metal and anion being chemically differentand said coating being formed and thermally associated at the thermalconditions of the inner core external surface.
 2. The article of claim 1wherein the metal of the metal oxyanion coating is selected from thegroup consisting of titanium, boron, silicon, aluminum, molybdenum,zirconium, tungsten, nickel, lanthenum and mixtures thereof.
 3. Thearticle of claim 2 wherein the metal is selected from the groupconsisting of titanium, boron, aluminum, molybdenum and silicon.
 4. Thearticle of claim 3 wherein the metal oxyanion coating is selected fromthe group consisting of metal oxynitride, metal oxysilicide and metaloxynitride.
 5. The article of claim 2 wherein the metal oxyanion coatingis selected from the group consisting of metal oxycarbide, metaloxysilicide and metal oxynitride.
 6. The article of claim 1 wherein theanion of the metal oxyanion coating is selected from the groupconsisting of carbide, boride, sulfide, silicide, and nitride.
 7. Thearticle of claim 6 wherein the anion is selected from the groupconsisting of nitride, boride, carbide.
 8. An article comprising athermally associated nondeleterious contaminated metal oxycarbide coatedthree dimensional powder particle substrate having an inner substratecore, a thermally reactive surface chemically different from said coreon at least a part of said inner core and a metal oxycarbide coatingthermally formed from said reactive surface, said metal and carbidebeing chemically different and said coating being formed and thermallyassociated at the thermal conditions of the inner core external surface.9. The article of claim 8 wherein the metal of the metal oxycarbidecoating is selected from the group consisting of titanium, boron,silicon, aluminum, molybdenum, zirconium, tungsten, nickel, lanthanumand mixtures thereof.
 10. The article of claim 9 wherein the metal isselected from the group consisting of titanium, boron, aluminum,molybdenum and silicon.
 11. The article of claim 8 wherein the metaloxycarbide coating is selected from the group consisting of siliconoxycarbide, titanium oxycarbide, molybdenum oxycarbide and zirconiumoxycarbide.
 12. The article of claim 11 wherein the metal oxycarbidecoating is selected from the group consisting of silicon oxycarbide andtitanium oxycarbide.
 13. The article of claim 12 wherein the metaloxycarbide coating is titanium oxycarbide.
 14. An article comprising athermally associated nondeleterious contaminated metal oxynitride coatedthree dimensional powder particle substrate having an inner substratecore, a thermally reactive surface chemically different from said coreon at least a part of said inner core and a metal oxynitride coatingthermally formed from said reactive surface, said metal and nitridebeing chemically different and said coating being formed and thermallyassociated at the thermal conditions of the inner core external surface.15. The article of claim 14 wherein the metal of the metal oxynitridecoating is selected from the group consisting of titanium, boron,silicon, aluminum, molybdenum, zirconium, tungsten, nickel, lanthanumand mixtures thereof.
 16. The article of claim 14 wherein the metal isselected from the group consisting of titanium, boron, aluminum,molybdenum and silicon.
 17. The article of claim 16 wherein the metaloxynitride coating is aluminum oxynitride.
 18. The article of claim 16wherein the metal oxynitride coating is boron oxynitride.
 19. Thearticle of claim 16 wherein the metal oxynitride coating is siliconoxynitride.
 20. The article of claim 14 wherein the metal oxynitridecoating is selected from the group consisting of aluminum oxynitride,silicon oxynitride, molybdenum oxynitride and titanium oxynitride.